1. Field of the Invention
The present invention relates to linear seat actuators, especially ones in which a threaded leadscrew rotates a gear nut as the lead screw translates. Stopping gear nut rotation prevents leadscrew translation. The present invention teaches an improved locking mechanism that positively secures the gear nut in such an actuator.
2. State of the Art
U.S. Pat. No. 5,689,995, entitled "Actuator that Adjusts to Side Loads Automatically by Pivoting Internally," and owned by P. L. Porter Co., the assignee of this application, teaches a linear actuator. It uses a leadscrew or threaded shaft that translates axially when a vehicle seat is reclined. As the leadscrew moves axially, a threaded gear nut or spin nut rotates about the leadscrew. The actuator has a mechanism that engages or disengages the gear nut when a user manually activates a recline lever. When the locking mechanism engages the gear nut and prevents gear nut rotation, the gear nut locks the leadscrew from further axial movement. Griswold, U.S. Pat. No. 5,320,413 (1994), Rees U.S. Pat. No. 4,881,775 (1989), and Periou U.S. Pat. No. 4,799,734 (1989), are other examples of patents teaching similar types of seat actuators.
The locking mechanism typically has a lever that can extend between adjacent teeth of the gear nut. When in that position, the lever blocks gear nut rotation. Several problems can occur. The lever may not come down exactly between the teeth. If that happens, the lever may not fully engage the gear nut. However, the actuator may appear to be locked. Later, relatively small forces on the leadscrew provide a torque on the gear nut that is sufficient to move the lever out of the gear nut. Moving the lever out of engagement with the gear nut can release the actuator. Applicant also is concerned that even if the lever properly engages the gear teeth, large forces may urge the lever out of the gear nut and release the actuator. Users of many prior art devices must cause a handle to rotate through a long distance to engage the actuator.